Para-xylene is an important base material in the chemical industry. It is generally required substantially free from other aromatic hydrocarbons and in particular from the isomeric compounds, ortho-xylene, meta-xylene, and ethylbenzene often produced during its manufacture. Since the four isomeric compunds closely resemble each other as regards their physical and chemical properties, the separation of para-xylene from such a mixture presents a particular problem.
While it is known from U.S. Pat. No. 3,729,523 to use crystalline silicates for the separation of para-xylene from the said mixtures, in practice a large quantity of ethyl benzene is also adsorbed by the silicate. The present invention seeks to improve the selectivity of the crystalline silicate for para-xylene over ethyl benzene.
It has now been found that the selectivity for para-xylene over ethyl benzene can be improved by using a modified crystalline silicate.